Gravity davit



May'25, 1943. w. ,a. we

GRAVITY DAVIT Filed June 12. 1942 5 Sheets-Sheet 1 INVENTOR. Wdldam E. filling BY FITTORIVEY May 25, 1943. we. ELLING GRAVITY mwm Filed June 12, 1942 5 Sheets-Sheet 3 INVENTOR. PW diam E. Elan/g TTORNEY May 25, 1943. w. E. ELLING emwmv mwm Filed Jun 12, 1942 5 Sheets-Sheet 4 :A TToR/vEY May 25, 1943. w. a. ELLlNG 2,319,354

' GRAVITY nAv'I'r Filed June 12, 1942 5 Sheets-Shaet 5 INVENTOR.

m1; am 5. 511m TTOENEY Patented May 25, 1943 UNITED STATES PATENT OFFICE GRAVITY DAVIT William E. Elling, Metuchen, N. J. Application-June 12, 1942, Serial No. 446,767

15Claims.

This invention relates to a new and useful improvement in gravity davits for use on ships. The gravity davits in use at the present time on ships are of the cradle and trackway type, and are, of course, used in pairs. The trackway generally stands vertically on the edge of the boatdeck and curves inboard at a height of about five feet to a 30 degree incline, which ends against the edge of the deck above. The stowage position of the boat, which is suspended from the cradle head, is about at the top deck level. The sheaves for the winch cable must be located at the top endof the trackway for a proper lead to operate the cradle, which must be pulled up the vertical part of the trackway and up the incline. This, of course, consumes much electric power. The cradle has two pairs of rollers which are located in the trackway, one above the other, and it is obvious that, in order to bring the cradle head far enough out for the proper outreach to clear the boat from the ship's side, both rollers must be lowered into the vertical section of the trackway. The power necessary for lifting the loaded cradle into stowage position is normally estimated as being twice the power necessary for the free lift of the boat before it reaches the cradle head.

Tests with the davit of this invention have shown that the additional power for moving the davit arm inboard can be regulated by the shape of the trackway for the inboard rollers, and may be much less than that required for present types of davits. However, it is desirable that the additional power should be about 25% so that the floating block to which the lifeboat is attached,

will engage the hook on the davit head before the davit begins to move inboard.

A dimculty with present-day gravity that, unless the floating block is held by some means other than the cable during the outboard travel of the davit, the davit will not run out and down. To the contrary, the pull of the boat will cause the davit to move inboard.

A well-known arrangement for holding the floating block is a hook so located that the block will just clear its end when the davit has reached launching position. This'arrangement will work as long as the ship is in upright position, but the rules for life saving in many countries specify that davits be made so t at boats may be launched when the ship is listed 15 towards the opposite side. In such case the floating block will not slide off the hook automatically.

The object of this invention is a davit for launching ships lifeboats by their own gravity,

which is simple in construction and in operation, and which requires very little extra power for recovering or hoisting the boat into stowage position.

davits is A further object is the provision of a gravity davit which will allow the stowage of the boat close to the boatdeck.

A still further object is a gravity davit which is secure in stowage position by having a long leg extending down in the davit base frame which is secured to the deck of the ship. This davit is simple in the operation of preparing for stowage, due partly to the fact that it is only necessary to have one pair of sheaves at the davit head, which, of course, would not be possible with a four-wheel cradle davit because the direction of the pull from davit head sheave to base frame would pull the cradle on a trackway which is inclined 30 down instead of up. With the davit of this invention the cable leading from the davit-head sheave to the base frame sheave will pull the davit into the vertical stowage position, and hold it in this position because it may be assumed that the lower wheels are bearing the entire weight of the davit and boat and the upper wheels are pressed against the upper flange of the track channels and thereby locking the davit securely.

Still another object of the invention is the provision of means for an easy start of movement by the combination of a pivoted davit leg and retarded engagement of the upper wheels after the start.

An important feature of the invention is the position of the trackways to each other. The upper trackway is inclined downward and outboard, and the lower trackway branches from its connection on the underside of the upper trackway pointing away from the direction of the upper trackway. This is helpful to the operation of the davit in several ways-first, the upper trackway wheels will be forced to roll down on the lower flange of the upper trackway channel, due to the boat weight, and, secondly, the lower trackway wheels will be forced to roll up on the upper flange of the lower trackway channels, also due to the boat weight.

In spite of the fact that it is necessary -to have a gravity davit operate with ease if the ship is listed to the opposite side by 15 degrees, it is possible with the davit of my invention to place the upper trackway comparatively flat and the lower trackway with an opposite inclination because the downward inclination of the upper track and upward inclination of the lower track may be added together for total effect. For example, if

the upper' track has an inclination of 30 degrees from the horizontal, and the lower track has an inclination of degrees, the effect is the same as if a four-wheel cradle were rolling on a 40 degree track.

Two forms of the davit of this invention are shown in the drawings, of which:

Figure 1 is a side elevation showing a davit and lifeboat in stowage position in full line an in launching position in dotted line;

Figures 2, 3 and a are diagrammatic views of this davit in three intermediate positions;

Figure 5 is a view of a modified form of davit;

Figure 6 is a diagrammatic view of the davit of Figure 5 provided with an automatic release for insuring that the floating block is released from the davit head when the davit is in launching position:

Figure 7 is a diagrammatic sectional view of the davit of Figure 6; and

Figures 8 and 9 are diagrammatic views illustrating' the operationof a swinging sheave at the davit head.

There are, of course, two davits per boat. They are identical so that only one need be described. As will be seen from Figure 1, the davit includes a deck frame consisting of a trackway post I, an upper trackway 2, and lower trackway I. The trackway post I may be of open box construction, as shown. Upper trackway 2 ex.- tends outwardly and downwardly from frame I, its lower end terminating at the edge of the boat deck to which it is attached. Preferably, the upper part 4 of upper trackway is inclined somewhat more sharply than midsection 5 to insure that the davit obtains a quick start from stowage position. The lower end of trackway 2 terminates in an elbow 6 of still greater pitch. The trackway may be made of two opposed angles or channels spaced far enough apart to permit the davit proper to pass between them.

Beneath trackway 2 is lower trackway 3, the inboardend of which may also be attached to frame I. This trackway also is inclined and terminatesin a short upwardly-directed leg I, which may be attached to the underside of trackway 2. This trackway may be made of two opposed channels with space enough between for the davit arm I. I

The inclination of trackways 2 and 3 may be varied considerably depending upon the conditions to be met. The major requisite is that the davit shall roll positively down the trackways even though the ship is listed degrees towards the opposite side. It is also highly desirable that the davit remain as nearly upright as possible during most of its launching movement so that the lifeboat can clear the deck from its low stow age position.

The davit proper consists of the long L-shaped arm 8, which is also provided with another shorter arm 9. At the lower end of arm 8 is a pair of rollers, one of which is shown at II), which roll in trackway 8. Arm 9 is also equipped with a pair of rollers, one of which is shown at I I, which roll in trackway 2.

At the davit head is a sheave I2 and in the davit arm 8, are two guide sheaves I3 and I4; a sheave I5 is carried by the top of frame I and another sheave III by the bottom of this frame. The hoisting cable II runs from the winch (not shown) through these sheaves to floating block I8 to which the lifeboat I9 is attached, and thence back over identical sheaves on the other side of the davit to an anchorage near the upper end of post I. In some cases it may be desirable to install a second sheave IS on the other side of post I, the cable being anchored to floating block II, thus providing a three-wire rope fall with a considerable saving in power required for hoistin The upper end of davit arm I is also provided with a hook by which floating block I8 is supported, as will be explained.

When thedavit is in its inboard position, davit arm I will be housed within frame I, as shown in full lines in Figure l. Lifeboat I9 is suspended from floating block II by its hanger 36, which hangs upon book 20. Practically all of the weight of the davit and lifeboat is supported by roller III on the-lower end of davit arm 8.

When the winch brake is released, the first movement of the davit is a swinging one upon roller ll, roller II on arm 9 at first swinging freely and then moving down trackway 2. Roller III will follow on trackway 8, so that the davit moves outwardly in substantially a vertical position, as shown in Figure 2. At this time floating block I8, and, consequently, the boat I9, is hanging on hook III. The direct lead in hook 20, and the resultant force of stress in the cable, are acting on opposite sides of the upper rollers II. Therefore, there is not much stress upon lower roller III.

As the davit continues to roll down the trackways, its vertical position is maintained, as shown in Figure 3, but when rollers II pass into the sharply inclined elbow 6, the davit will swing outwardly as shown in Figure 4. Before rollers II have reached the position shown in Figure 3, the resultant of the forces in the cable, as indicated in the drawing, obviously acts against the downward movement because its angle with the trackway is still greater than degrees, and, therefore, the downward movement is actuated only by the lifeboat weight hanging on the hook. When rollers II pass the knuckle at upper end of elbow 6, the angle between resultant force and elbow, 6 is less than 90 degrees. and, therefore, the floating block I8 will be lifted off hook 20 and pulled against the davit head.

When rollers I I have reached the lower end of elbow 6, rollers I. will have reached the end of trackway 3, and will then swing upwardly upon rollers I I as a pivot intov leg 1 until they reach the end of leg I. This causes the davit to swing into its ultimate launching position, as shown in dotted line in Figure 1. Since the resultant force of the boat and horizontal pull is outboard of rollers I I, there is no possibility that the davit will roll back up the trackways of its own accord. To the contrary, it is locked securely in launching position by rollers III in leg I of trackway 3.

When recovering a boat from the water, the davit maintains its launching position until floating block I8 has been pulled against the davit head. Then the davit first swings upon rollers II, until rollers I II have moved downwardly'out of leg I of trackway 3 after which it moves up the trackwaysuntil it gains its initial stowage position shown in full line in Figure 1. After rollers I I have moved out of elbow 6, the floating block I. will be automatically lowered onto book 20, because the resultant force is acting upon rollers II in a similar, but reversed, manner from that described for the downward movement.

When the davit is in stowage position, the

ample, davit arm I may be provided with an eye 2la, as shown in Figure 1, adapted to register with an eye 2| on the davit frame. Pin 22 can then be passed through eyes 2i and lid to lock the davit arm to the frame.

A modified form of the invention is shown in Figure 5. The difference resides chiefly in upper trackway 23, which is of the same inclination throughout. Its mode of operation is, in general, the same as that of the form first described, and will be understood without detailed description. However, unless the trackway 23 has a decidedly increased slope, which would raise the stowage position of the boat and increase the power required for recovery, there is a possibility that if the boat were hanging free, the resultant of the two cable forces would oppose the downward movement of rollers ,I I, so that the davit might be caused to run up the track. To

avoid this, hook should be long enough that floating block I8 will not be released until the davit has reached launching position, i. e., until rollers ill have been swung up into leg 'i of trackway 3, causing the davit to swing outward to its extreme position shown in dotted line in Figure 5.

A hook of this length-might not release the floating block automatically under all conditiOns-if the ship were listed in the opposite direction, for example. Therefore, some releasing means should be provided. One is shown in Figure 5. Davit head sheave 25, instead of being mounted directly on the davit head, as in Figure 1, is swung from the davit head by a link 25, which terminates in a handle 26. If the floating block I8 will not clear hook 20 when the davit has reached launching posit-ion,'handle 25 can be pushed outwardly. This will move sheave 24 outwardly also, and cause floating block [8 to clear the hook 20.

Secondly, the hanger of the floating block for engaging the davit-head hook will, of necessity. always be on the vertical tangent line of sheave circumference and load, and this will make it possible to choose the distance between pin 31 and pin 38, which is the center of the sheave,

so that the hook for the floating block hanger may be located at the exact spOt where all lines tangent to the sheave circumference meet in any of the positions the sheave amumes during the run from stowage to extreme outboard position. These tangent lines are designated as 39, 40, H and I2 inFigures 8 and 9. All meet at a point 43 and the hook may, therefore,,be very short.

Thirdly, the swinging davit-head sheave will make it possible to make the davit shorter and still retain the same outreach. This distance may easily amount to 4 inches in a medium sized davit.

If desired, an automatic device may be substituted for handle 26. One carried by davit arm 8 is shown in Figure 6, which consists of a bell crank composed of levers 21 and 28, pivoted at 29. The free end of lever 21 is adapted to engage a suitable cam fixed in trackway 3, so that it will be rocked outwardly when the davit reaches its outboard position. To lever 29 is preferably connected a rod 3 I, which in turn connects a second bell crank 32, and through it is connected to a second rod 33. Rod 33 connects with a rock lever 34, the free end of which projects below hook 20 and normally lies behind it.

When the davit with floating block I8 hanging from hook 20 reaches its outboard launching posit'on, the operation of this device will swing the lower end 35 of rock lever 34 outward so that it will push the hanger 36 of floating block I8 oif hook 20, thereby freeing it and the boat so that it can be lowered away. Preferably the handle 26 is provided even when the automatic" board ends in downwardly and upwardly extending elbows, respectively, a davit arm supported by outboard rollers adapted to travel along said upper trackway and by inboard rollers adapted to travel along said lower trackway, said inboard rollers being capable of swinging up into said elbow of said lower trackway when said outboard rollers have reached the terminus of the elbow of said upper trackway.

2. In a gravity davit an upper trackway sloping downwardly in outboard direction, a second trackway below said upper trackway having at its outboard end an upwardly extending elbow, a davit arm supported by outboard rollers adapted to travel along said upper trackway and by inboard rollers adapted to travel along said lower trackway, said davit arm being adapted to swing upon said inboard rollers as a pivot at the start of its outboard movement and upon said outboard rollers as a pivot at the completion of its outboard movement.

3. In a gravity davit an upper trackway sloping downwardly in outboard direction, a second trackwaybelow said upper trackway, a davit arm supported by outboard rollers adapted to travel along said upper trackway and by inboard rollers adapted to travel along said lower trackway, said trackways being so shaped and positioned relative to each other as to cause said davit arm to move in outboard direction in substantially upri ht prsition and to swing outwardly into a materially inclined position after completion of its outbcard movement along said trackways.

4. In a gravity davit an upper trackway sloping downwardly in outboard direction, a second trackway below said upper trackway, a davit arm supported by outboard rollers-adapted to travel along said upper trackway and by inboard rollers adapted to travel along sa d lower trackway,

means in said upper trackway to cause said davit arm to swing outwardly at the end of its outboard travel, and means in said lower trackway to permit said davit arm to swing still further outwardly after the completion of its outboard travel.

5. In a gravity davit an upper trackway sloping downwardly in outboard direction, a second trackway below said upper trackway, a davit arm supported by outboard rollers adapted to travel along said upper trackway and by inboard rollers adapted to travel along said lower trackway, and means in said t-rackways to permit said davit arm to swing outwardly at the completion of its outboard travel;

6. In a gravity davit an upper trackway sloping downwardly in outboard direction, a second trackway below said upper trackway, a davit arm supported by outboard rollers adapted to travel along said upper trackway and by inboard rollers adapted to travel along said lower trackway, and means in said lower trackway to permit said davit arm to swing outwardly at the end of its outboard travel and to oppose inboard movement by it while in its outboard position.

' arm to swing outwardly at the end of its outboard travel, and means in said lower trackway to permit said davit arm to swing still further outwardly after the completion of its outboard travel, sheaves rotatabLv mounted on the outboard end of said davit arm, a hook in said davit arm below said sheaves for supporting the hanger of a floating block and adapted to release said hanger when said davit has assumed its ultimate outboard position.

8. In a gravity davit an upper trackway sloping downwardly in outboard direction, a second trackway below said upper trackway, a davit arm supported by outboard rollers adapted to travel along said upper trackway and by inboard rollers adapted to travel along said lower trackway, means in said upper trackway to cause said davit arm to swing outwardly at the end of its outboard travel and means in said lower trackway to permit said davit arm to swing still further outwardly after the completion of its outboard travel, sheaves swingably supported on the outboard end of said davit arm, a hook on said outboard end of said davit arm to support the hanger of a floating block, and means for swingingsaid sheaves manually outwardly to release said hanger from said hook.

9. In a gravity davit an upper trackway sloping downwardly in outboard direction, a second trackway below said upper trackway, a davit arm supported by outboard rollers adapted to travel along said upper trackway and by inboard rollers adapted to travel along said lower trackway, means in said lower trackway to permit said davit arm to swing outwardly after the completion .of its outboard travel, sheaves swingably supported on the outboard end of said davit arm, a hook on said outboard end of said davit arm adapted to support the hanger of a floating block, and means associated with said davit arm and 'operated by the movement thereof to automatically release said hanger from said hook when said davit arm reaches its outboard position.

10. In a gravity davit an upper trackway having an inboard section which slopes downwardly relatively steeply in outboard direction, a midsection which slopes less steeply, and an outboard section which slopes more steeply than the mid-section, a second trackway below said upper trackway, a davit arm supported by outboard rollers adapted to travel along said upper trackway and by inboard rollers adapted to travel along said lower trackway, said davit arm being adapted to swing upon said inboard rollers as a pivot at the start of its outboard movement and upon said outboard rollers as a pivot at the completion of its outboard movement.

11. In a gravity davit an upper trackway having an inboard section which slopes downwardly relatively steeply in outboard direction, a midsection which slopes less steeply and an outboard section which slopes more steeply than the mid-section, a second trackway below said upper trackway having at its outboard end an upwardly extending elbow, a davit arm supported by outboard rollers adapted to travel along said upper trackway and by inboard rollers adapted to travel along said lower trackway, said davit arm being adapted to swing upon said inboard rollers as a pivot at the start of its outboard movement and upon said outboard rollers as a pivot at the completion or its outboard movement.

12. In a gravity davit an upper trackway sloping downwardly in outboard direction, a second trackway below said upper trackway, a davit arm supported by outboard rollers adapted to travel along said upper trackway and by inboard rollers adapted to travel along said lower trackway, means in said lower trackway to permit said davit arm to swing outwardly after the completion of its outboard travel, sheaves swingably supported on the outboard end of said davit arm, a hook on said outboard end of said davit arm adjacent the top of said sheaves to support the hanger of a floating block, and means for swinging said sheaves manually outwardly to release said hanger from said hook.

13. In a gravity davit an upper trackway sloping downwardly in out-board direction, a second trackway below said upper trackway having at its out-board end an upwardly extending elbow, a davit arm supported by out-board rollers adapted to travel along said upper trackway and by in-board rollers adapted to travel along said lower trackway, said trackways being so shaped and proportioned relative to each other as to permit' said davit arm to move in out-board direction in substantially upright position and to swing outwardly into a materially inclined position after completion of its out-board movement along said trackways.

14. In a gravity davit a davit arm supported by in-board and out-board rollers, trackways engaged by said rollers adapted to permit said davit arm to move in out-board direction and to swing outwardly into a materially inclined position after completion of its out-board movement, a sheave swingably supported on each side of said davit arm at its out-board end, a floating block having a hanger, a hook on said out-board end of said davit arm to .support said hanger, and means for swinging said sheaves manually outwardly to release said hanger from said hook.

15. In a gravity davit an upper trackway sloping downwardly in out-board direction, a second trackway below said upper trackway, a davit arm supported by out-board rollers adapted to travel along said upper trackway and by in-board rollers adapted to travel along said lower trackway, means in said lower trackway to permit said davit arm to swing outwardly after the completion of its out-board travel, a hook on said outboard end of said davit arm adapted to support the hanger of a floating block, and means associated with said davit arm and operated by the movement thereof to automatically release said hanger from said hook when said davit arm reaches its outboard position. 4

WILLIAM E. ELLING. 

